Magnesium surface enrichment of CoFe2O4 magnetic nanoparticles immobilized with gold : reusable catalysts for green oxidation of benzyl alcohol

Abstract

Gold nanoparticles have shown excellent activity for selective oxidation of alcohols; such catalytic systems are highly dependent on the initial activation of the substrates, which must occur on the catalyst surface in heterogeneous catalysts. In many cases, an extra base addition is required, although the basicity of the support may also be of significant importance. Here, we explored the intrinsic basicity of magnesiumbased enrichments on CoFe2O4 magnetic nanoparticles for the oxidation of benzyl alcohol using molecular oxygen as oxidant. The MgO and Mg(OH)2 enrichments enabled gold impregnation, which was not possible on the bare CoFe2O4 nanoparticles. The Au/MgO/CoFe2O4 and Au/Mg(OH)2/CoFe2O4 catalysts reached 42% and 18% conversion, respectively without base promotion, in 2.5 hour and 2 bar of O2. When the catalysts were tested with sub-stoichiometric amounts of base, they became more active (>70% of conversion) and stable in successive recycling experiments without metal leaching, under the same reaction conditions. We also showed the oxide phases of the enrichments performed using Rietveld refinements and how the Mg(OH)2 phase interferes with the activity of MgO-based materials.